1. Field Of The Invention
The present invention relates to a printing apparatus and more particularly to a paper feeding apparatus for feeding a printing sheet separately from stacked sheets.
2. Related Art
In one example of a conventional sheet feeding apparatus for use in a printer, as disclosed in Japanese Patent Publication No. Sho. 58-6633, a printing sheet is fed with a platen rotating in the reverse direction, and even after a front end of the printing sheet reaches a nipping region of the platen and a driven roller to stop forwarding further the printing sheet is forced to be fed further so that the printing sheet is bent to thereby eliminate an undesirable skew, and then the platen is controlled to rotate in the forward direction so that the printing sheet is transported to the printing start position.
On the other hand, Japanese Patent Publication No. Sho. 62-38261 discloses another arrangement in which a printing sheet is fed separately by a pick-up roller rotating forwardly to a pair of drive rollers rotating forwardly, a sensor detects a condition of the printing sheet that a front end of the printing sheet passes completely through the pair of rollers and afterwards the pickup roller is stopped rotating while the drive roller is rotated in the reverse direction until the front end of the printing sheet is pushed out of the pair of drive rollers to thereby bend the printing sheet and so that an undesirable skew is eliminated. Afterwards, the pair of drive rollers are again rotated in the forward direction to transport the printing sheet to a printing position.
In the conventional printing apparatus for feeding a printing sheet as disclosed in the Japanese Patent Publication No. Sho. 58-6633 shown in FIG. 10, the front end of the printing sheet is abutted against the driven roller 102 and the platen 101 while they are rotating in the reverse direction as shown in FIG. 10A. Therefore, if the condition which the front end portion of the printing sheet 106 abuts against the platen 101 and driven roller 102 is irregular as shown in FIG. 10B, the front end portion of the printing sheet 106 may be wound on the roller, or folded as shown in FIG. 10C. Further, the bending (or slackening) operation applied to the printing sheet is performed only by rotating the paper feeding roller in the forward direction while checking the advance the front end portion of the printing sheet. Hence, if the printing sheet is large in thickness, it is difficult to sufficiently bend the same, and it takes a relatively long period of time to bend the sheet, with the results that the printer is lowered in through-put and in reliability.
In the conventional apparatus taught in Japanese Patent Publication No. Sho. 62-38261, the printing sheet is once fed until the sheet passes completely through the pair of drive rollers to detect such a condition of the printing sheet with the sensor and then the pair of drive rollers are controlled to rotate in the reverse direction and, further, in bending the printing sheet by turning the drive roller in the reverse direction, the sheet feeding roller is held stopped as described above. Hence, the printing sheet must be bent only by turning the drive roller in the reverse direction. For this reason, it takes a long time period and accordingly the through-put is lowered. Furthermore, in the case of a printing sheet relatively large in thickness, the roller may slip, so that the printing sheet cannot be sufficiently bent, with the result that the printer is lowered in reliability.